Conditioning of organic pigments

ABSTRACT

Organic pigments are conditioned by treating them, after synthesis but preferably without or with only partial drying, in a mixture of from 1 to 30% by weight of a neutral, polar liquid having a dipole moment μ of 2.8-6.0? 10 −18  esu (2.8 to 6.0 debye units) and from 70 to 99% by weight of water in an agitated media pearl mill having a specific power density of at most 2.0 kJ s?−1  per liter of grinding space. Drying is especially suitable in the case of only slightly agglomerating, easy to wet pigments of specific surface area from 1 to 25 m 2 /g. The method gives excellent results, and is flexible and also much simpler than known methods.

The invention relates to a simplified, economical and environmentallyfriendly method of conditioning organic, especially polycyclic pigmentsand diketopyrrolopyrroles. The coloristic properties of the pigmentsobtained are significantly better than in the case of existing simplemethods and as good as in the case of known methods that are morecomplicated, more costly, or problematic.

Pigments are generally obtained from synthesis in a form that is notsuited, or is only poorly suited, to most applications. It is thereforecustomary for the crude pigments to be subjected to conditioning. In thecourse of time it has also been found that most conditioning methods arehighly specific and can be used only for individual pigment classes oreven only for individual pigments, giving rise, therefore, to virtuallycountless methods, which have been disclosed in an extremely largenumber of patent applications and patents.

In such methods, the same basic principles are always applied: the crudepigments are dissolved and re-precipitated from the solution, ground(where appropriate, with the aid of grinding elements), or treated withwater or solvents (where appropriate, at elevated temperature).Generally, however, the methods are combined with one another and, whereappropriate, supplemented by additional process measures havingdifferent purposes, for example the addition of acids, bases and/oradditives, giving rise to the many known variants.

In particular, the patents and patent applications which are consideredhereinbelow appear representative of those existing methods.

In U.S. Pat. No. 2,857,400 and U.S. Pat. No. 3,017,414, pigments arefirstly dry-ground and then stirred vigorously in a solvent (includingdimethylformamide) or in an emulsion consisting of water and a non-polarsolvent. U.S. Pat. No. 4,431,806 uses, inter alia, N-methylpyrrolidone,with addition of water and heating to 50° C. being carried out beforefiltering. From EP-A-0 524 904 and U.S. Pat. No. 5,264,034, it isapparent that, for aftertreatment of previously ground crude products,polar solvents, including especially dimethyl sulfoxide andN-methylpyrrolidone, are suitable at temperatures of up to about 50° C.as suspension media also for further pigment classes.

The procedure in U.S. Pat. No. 5,492,563, for phthalocyanines, is also atwo-stage procedure wherein, after the necessary comminution by means ofdry grinding (with addition of wax), the aftertreatment is carried outin water together with up to 5% of an organic solvent. Polar solventsare also disclosed, methyl ethyl ketone being used in one example. Incontrast, in Example 3 of U.S. Pat. No. 5,614,014, coarse-grained,unsubstituted γ-quinacridone is, without prior comminution, ground in10% dimethylformamide with application of a high force and at a highradial speed at 25° C., but, undesirably, opacity is not achievedwithout aftertreatment (finishing) as in Example 9. According to U.S.Pat. No. 4,094,699, in the case of quinacridones, organic liquids neednot be used during wet grinding if a wetting agent together with astrongly alkaline aqueous solution is used.

In U.S. Pat. No. 3,615,800, perylenes are obtained by grinding the dryreaction product in slightly polar solvents at temperatures of from −10°C. to at most 50° C. In contrast, U.S. Pat. No. 4,895,948 and U.S. Pat.No. 4,895,949 disclose methods that are suitable for quinacridones,wherein a strongly alkaline, aqueous alcohol is used at from 20° C. to40° C. According to U.S. Pat. No. 4,922,101, it is possible to proceedin the same manner for diketopyrrolopyrroles, in which case thetemperature is likewise below 50° C. In contrast, according toWO-A-99/54410, treating pre-ground copper phthalocyanine in a stronglyalkaline, aqueous alcohol results in a phase transformation.

On the other hand, in order to avoid dust formation, U.S. Pat. No.5,318,627 uses water or solvents (including polar solvents) both forgrinding and for optional subsequent after-treatment of crudecarbazoledioxazine (a crude material known to be especially coarse andhard), although the examples are confined to water, diethylene glycoland, especially, isobutanol. In EP-A-0 971 001, quinacridones are groundin an organic solvent (including, for example, dimethylformamide) andthen, optionally, subjected to aftertreatment also in an organic solventat from 50 to 200° C.

Example 9 of U.S. Pat. No. 3,256,285 discloses the treatment of anaqueous press cake of 2,9-diphenoxy-quinacridone with ethanol at 150° C.under pressure. The ratio of water to ethanol is 43:57. Identicalresults are also said to be obtained using N-methylacetamide. In neutralwater, according to U.S. Pat. No. 3,287,147, solid solutions ofquinacridones are also obtained at from 150° C. to 300° C. Analogously,in Example 12 of U.S. Pat. No. 5,428,136, a wet azo pigment press cakeis treated with a mixture of isobutanol and water at 150° C. U.S. Pat.No. 5,756,691 discloses the subsequent treatment of a further wet azopigment in a large excess of N-methylpyrrolidone at 130° C. On the otherhand, according to U.S. Pat. No. 6,191,263, treating a calcium azo lakepigment with 30.8% to 20.4% (decreasing concentration)N-methylpyrrolidone in water at 90° C. results in a change in thecrystalline form. In U.S. Pat. No. 4,024,148, a water-insoluble,hydroxyl-containing solvent is used under reflux.

In numerous methods, pigments are first dissolved to produce clearsolutions, for example in concentrated sulfuric acid or a polar solventsuch as dimethylformamide, dimethyl sulfoxide or N-methylpyrrolidonewith the addition of a small amount of a strong alkali (at most 20%water, based on the liquid phase). The solution of colorant is thendiluted with dilute acid, water or an alcohol or is added thereto, thecrystalline form obtained being critically dependent upon the preciseprecipitation conditions. For example, quinacridones (U.S. Pat No.4,247,696, JP-A-54/130621, JP-A-58/147461), and also azos andthioindigos (U.S. Pat. No. 4,734,137) as well as diketopyrrolopyrroles(U.S. Pat. No. 5,565,578, EP-B-0 737 723) can be treated in that manner.

All these methods are, for various reasons, not entirely satisfactory;moreover, such methods can be transferred from one pigment to anotheronly with difficulty. In the case of multifunctional pigment plants,that results in high investment costs, a high personnel requirement, alack of operational flexibility and extremely complex and costly qualityassurance measures.

Some of those problems can be avoided by subjecting the dry crudepigments to salt kneading in a separate system with the addition of asmall amount of solvent. The procedure is, however, slow, noisy and veryenergy-consuming. In addition, because of the very high frictionalenergy, it is necessary to monitor continuously the temperature (with agreat deal of cooling) and the viscosity of the paste and, subsequently,solvent-containing brine must be disposed of in an environmentallyfriendly manner. In addition, further purification steps are necessaryto achieve the low conductivity required, for example, for electronicapplications.

There has now been found, surprisingly, a simple conditioning methodwhich can be used for very many organic pigments and which ensures aconsiderable increase in productivity together with a very high qualityof final product.

The invention accordingly relates to a method for the preparation of aconditioned pigment, wherein

-   -   (1) the pigment is so synthesised that it precipitates from a        liquid reaction mixture, and a pigment suspension is formed in        the liquid reaction medium;    -   (2) optionally, the concentration of pigment in the pigment        suspension is increased by removing part of the liquid reaction        medium;    -   (3) optionally, a washing agent is added once or more than once        and then the concentration of pigment in the pigment suspension        is increased by removing part of the liquid phase;    -   (4) the pigment suspension from step (1), the concentrated        pigment suspension from step (2), or the pigment suspension        (treated with a washing agent and concentrated) from step (3),        the liquid phase of which consists substantially of water, a        neutral, polar liquid or a mixture thereof, is transferred into        a storage vessel, optionally with addition of water or a        neutral, polar liquid having a dipole moment μ of 2.8-6.0·10⁻¹⁸        esu, keeping the pigment surface substantially wetted with        liquid reaction medium, washing agent, polar liquid or water all        the time;    -   (5) if the liquid phase of the pigment suspension in the storage        vessel does not already consist of water and a neutral, polar        liquid, the amount of neutral, polar liquid being from 1 to 30%        by weight, based on the total amount of liquid and water, the        composition of the pigment suspension is so modified by means of        the addition of water or neutral, polar liquid having a dipole        moment μ of 2.8-6.0·10⁻¹⁸ esu that the amount of neutral, polar        liquid is from 1 to 30% by weight, based on the total amount of        liquid and water;    -   (6) the pigment suspension from the storage vessel is passed a        number of times through an agitated media pearl mill in a        circulating or shuttle mode of operation, the agitated media        pearl mill having a smaller chamber volume than the volume of        the pigment suspension and being operated at a specific power        density of at most 2.0 kj·s⁻¹ per liter of grinding space;    -   (7) optionally, the concentration of pigment in the pigment        suspension from the agitated media pearl mill is increased by        removing part of the liquid reaction medium;    -   (8) optionally, a washing agent is added once or more than once        to the pigment suspension from step (6) or (7) and then the        concentration of pigment in the pigment suspension is increased        by removing part of the liquid phase; and    -   (9) the pigment is isolated by removing the liquid surrounding        it.

Step (1) corresponds to pigment synthesis known per se to the personskilled in the art but stopped at the point where the reaction iscomplete. Subsequent maturation may optionally be carried out, forexample in order to increase filterability, but that should be carriedout under mild conditions so that the pigment particles do not becometoo large. Generally, the average size of non-agglomerated primaryparticles, viewed with an electron microscope, should be from 0.01 to 3μm, preferably from 0.05 to 2 μm. It is essential to the invention, atany rate, that the pigment particles are generally not dried; otherwise,they aggregate and the desired result cannot be achieved or is achievedtoo slowly.

Although not desirable, it is, exceptionally, possible to use a driedpigment in the case of very coarse pigments that have only a very slighttendency to aggregate and are easy to wet with water or a polar solvent,for example crude pigments having a specific surface area of from 1 to25 m²/g, especially from 2 to 15 m²/g. Dried pigments preferably stillcomprise a residual amount of water or a neutral, polar liquid, forexample from 0.1 to 20% by weight, most preferably from 1 to 10% byweight. Apart of the additional drying and wetting steps, however, thisprocedure is in all particulars similar to that described above and thesame preferences do apply.

Increasing the concentration of pigment in the pigment suspension insteps (2), (3), (7) and/or (8) can be carried out by methods known perse, for example filtration, dialysis or sedimentation with removal ofliquid from the clear phase, optionally under increased gravity. ‘Part’is to be understood as an amount of from 1 to 99% by weight, usuallyfrom 1 to about 90% by weight.

Washing agents suitable for step (3) will be known to the person skilledin the art from the relevant synthesis methods for the pigment used.They are, for example, water, brine, bicarbonate solution or any desiredorganic solvent, alone or in admixture or in any desired order. Thepurpose of such washing is to remove unreacted starting materials,reagents and by-products, especially acids, bases and colouredby-products. If filtration is used in step (2), it is especiallyefficient and advantageous to rinse the wet filter cake with washingagent. It is of course also possible first to redisperse the filter cakein the washing agent and only then to filter again.

The pigment suspension can be transferred to the storage vessel bymethods known per se, which will depend on the consistency of thepigment suspension. A low-viscosity pigment suspension can, for example,be pumped, a solid press cake can be transferred by scooping or tipping,and a viscous paste by flushing with water or solvent. A particularaspect of the invention relates to transferring the pigment suspensionin the form of a press cake consisting of from 10 to 50% by weightpigment and from 50 to 90% by weight liquid, preferably from 20 to 40%by weight pigment and from 60 to 80% by weight liquid. In that case theliquid is a neutral polar liquid having a dipole moment μ of2.8-6.0·10⁻¹⁸ esu, water or a mixture thereof, preferably water.

Step (5) specifies suitably modifying, when necessary, the ratio ofwater to neutral, polar liquid before passage through the agitated mediapearl mill. If a neutral, polar liquid having a dipole moment μ of2.8-6.0·10⁻¹⁸ esu (2.8 to 6.0 debye units) is added in step (5), that iscarried out preferably before step (6) is started. It is also, however,perfectly possible to add all or some of the neutral, polar liquid tothe pigment suspension only after one or more passes through theagitated media pearl mill, although the treatment time will beneedlessly extended as a result.

The treatment of the pigment suspension in the agitated media pearl millis an essential step of the invention. The friction must not be toohigh; otherwise, pigment particles that are obtained will be too smallas a result of the grinding action. Conversely, the speed must not betoo low; otherwise, the dispersive force will be insufficient toseparate any agglomerations present into their primary particles. It hasbeen found that the specific power density should be at most 2.0 kj·s⁻¹per liter of grinding space and the peripheral speed of the agitatorshould then be from 5 to 12 m·s⁻¹, preferably from 6 to 11 m·s⁻¹. Higherperipheral speeds of up to about 15 m·s⁻¹ (perhaps even higher in thefuture) are possible with some special apparatus, but only if achievableat a specific power density of at most 2.0 kj·s⁻¹ per liter of grindingspace.

The temperature is advantageously in the range between the freezingpoint and the boiling point of the mixture of water and polar liquid,preferably from 20 to 80° C., especially from 50 to 80° C. An especiallypreferred aspect of the invention relates to the use, under excesspressure, of a temperature of from 70 to 120° C., especially from 100 to120° C. The temperature is advantageously adjusted in the storagevessel. Temperature control can be achieved especially conveniently inthe temperature range from 50 to 80° C. because the heat of friction canbe balanced, approximately, by the heat losses. Above that range, it isnecessary to carry out heating; alternatively, however, a particularaspect of the invention relates to lowering the temperature in thecourse of grinding from the above-mentioned initial value to a valuefirst of from 50 to 80° C. and then at the end of grinding from 20 to50° C.

The agitated media pearl mill is a known apparatus, it merely beingnecessary to use a controller so that, at full power, it does not exceedthe above-mentioned specific power density. Whilst taking thatprecaution, it is possible to use any desired apparatus, withoutrequiring any special constructional measures because the heat offriction is not very great. In other regards, the operating instructionsof the available apparatus should be consulted. As grinding elementsthere are used, for example, balls of from 0.1 to 1 mm in diameter madefrom zirconium oxide, mixed zirconium oxide, aluminium oxide, quartz ora metal such as steel, preferably mixed zirconium oxide balls having adiameter of from 0.2 to 0.3 mm.

The treatment period in the agitated media pearl mill is usually from 20to 200 minutes (including dwell time in the storage vessel betweenindividual passes), a longer treatment period having no significanteffect on the properties of the product. As a result, the risk ofovermilling can be excluded, with very great advantage for the meetingof specifications, especially if it is ensured that the radial speed ofthe mill is not too high; in the final phase of grinding (approximatelythe last third of the total grinding time), the radial speed should becut back to a value of at most 11 m·s⁻¹, preferably from 1 to 8 m·s⁻¹,especially from 2 to 5 m·s⁻¹.

In the case of a shuttle mode of operation, a plurality of storagevessels is used, for example from 2 to 20 storage vessels, thesuspension being passed from one storage vessel to another storagevessel via the agitated media pearl mill.

Passing pigment suspension through a number of times in a circulating orshuttle mode of operation is understood to mean that the volume passedthrough is at least twice as great as the volume of the pigmentsuspension, which in the shuttle mode of operation corresponds topassing through approximately twice. The maximum value is arbitrary,although the use of more than one hundred passes, for example onethousand passes, whilst possible, is of little advantage because it hasno significant effect on the properties of the product. Circulating andshuttle modes of operation can also be combined with one another, forexample grinding first in a circulating mode of operation and then in ashuttle mode of operation and vice versa.

In principle, the washing agents used in step (8) can be the same as instep (3). Because the conditioning according to the invention is carriedout substantially under neutral conditions, it is necessary to remove,at most, very small amounts of acid or base. Moreover, once step (3) hasbeen carried out, most of the unreacted starting materials, reagents andby-products will already have been removed so that smaller amounts ofpolar solvents, for example alcohols and, preferably, water, can be usedfor the washing.

Isolation of the pigment is carried out by any desired known method. Forexample, it is possible to carry out filtration or centrifugation andthen to dry the moist material in an oven or fluidised-bed apparatus(for example at from 50 to 250° C., optionally in vacuo), or tofreeze-dry it. It is likewise possible to spray-dry the pigmentsuspension directly. The conditioned pigment is usually obtained in theform of a powder, which can, if desired, be dry-ground and sieved ortreated by any other desired physical method.

The neutral, polar liquid advantageously has a dipole moment 1 of2.8-6.0·10⁻¹⁸ esu, measured in benzene at 25° C., preferably3.3-5.5·10⁻¹⁸ esu, especially 3.8-5.0·10⁻¹⁸ esu. The liquid should alsobe inert with respect to the pigment and to water at temperatures up to100° C. and also, in the concentration used and in the temperature rangeused, should dissolve in water to give a clear solution, although thatis virtually always the case. Suitable neutral polar liquids are, forexample, acetamide, formamide, methylacetamide, methylformamide,caprolactam, valerolactam, 1,1,2,2-tetramethylurea, dimethyl sulfoxide,sulfolane, nitromethane, nitrobenzene, acetonitrile, methanol, ethylenecarbonate, dimethylacetamide, dimethylformamide and N-methylpyrrolidone,preferably dimethyl sulfoxide (DMSO), dimethylformamide (DMF) orN-methylpyrrolidone (NMP), especially N-methylpyrrolidone.

Of course, slight molecular modifications of the above-mentioned liquidsare possible (for example, replacement of methyl groups by ethyl groups)provided that their polarity remains suitable as a result. Optionally,it is also possible to use mixtures of a plurality of neutral liquids,the overall polarity of which lies in the specified range of2.8-6.0·10⁻¹⁸ esu (the overall polarity of a mixture of polar liquids,where applicable, should be calculated from the dipole moments of thecomponents in proportion to the relative amounts thereof in themixture).

The expression “liquid” is used herein because the pigments are, underneutral conditions, poorly soluble therein and therefore the usual term“solvent” would be functionally incorrect.

The amount of neutral, polar liquid is advantageously from 1 to 30% byweight, based on the total amount of liquid and water. Preference isgenerally given to an amount of liquid of from 3 to 20% by weight,especially from 5 to 10% by weight. For pigments having more thannegligible solubility in water (from 10 to 300 mg/l—for example, lakedazo pigments), the recommended amount of liquid is, however, from 0.5 to10% by weight. For colorants of still higher solubility in water, themethod is less suitable.

In addition, it is possible to use small amounts of additionalsubstances, for example acids, bases, resins, growth inhibitors and,especially, dispersing agents or wetting agents. The amount of acid orbase should, however, be at most 0.01 mol, especially at most 0.001 mol,based on 1 mol of water. Resins are added in amounts of up to, at most,10% by weight, preferably at most 5% by weight, especially 1% by weight,based on the pigment. Growth inhibitors and dispersing agents will beknown to the person skilled in the art and may be, for example,substances having structural elements of the pigment; they are usuallyused in amounts of at most 0.03 mol, based on 1 mol of pigment. Wettingagents, for example cationic, anionic, amphoteric or non-ionic wettingagents, can likewise be added in customary amounts. Preference is given,in that case, to the addition of from 0.2 to 5% by weight, especiallyfrom 0.5 to 3% by weight, based on the pigment, of an amphoteric wettingagent. Additional substances can suitably be added in any step (1), (2),(3), (4), (5), (6), (7) or (8), preferably in step (6), (7) or (8), withparticular preference in step (6), especially after two-third of thetotal duration of step (6).

A major advantage of the invention is that no solid salts are necessary.Although it is possible to add salts (for example sodium chloride orsodium sulfate) up to the saturation limit in the aqueous liquid, thatdoes not bring about any advantages but, on the contrary, only givesrise to additional problems in recovering the liquid.

The method can be performed in the presence of air. In the case ofoxidisable pigments, for example quinacridones, it is, however,advantageously possible, if desired, to create inert conditions verysimply using nitrogen, carbon dioxide or a noble gas.

It is self-evident that, for the purpose of recycling, the neutral,polar liquid used can be recovered by methods known per se, for exampleby distillation.

In contrast to other conditioning methods, for example kneading, theviscosity plays a rather subordinate role. It is necessary, however, toselect a viscosity range that is suitable for the apparatus used, forexample from 5·10⁻² Pa·s to 5 Pa·s, preferably from 10⁻¹ Pa·s to 5·10⁻¹Pa·s (at 500 s⁻¹). The person skilled in the art will know, or candetermine by simple means known to him, how the viscosity depends uponthe temperature, the liquid selected and the concentration thereof, andupon the concentration and particle shape of the pigment beingconditioned.

The amount of crude pigment is usually, in step (6), from 1 to 25% byweight, preferably from 2 to 20% by weight, especially from 5 to 15% byweight, based on the total amount of crude pigment, liquid and water(including water or liquid in the press cake), it being necessary ofcourse for the amount of crude pigment to be calculated from the crudepigment content of the press cake because the press cake should not bedried. The amount of crude pigment in a press cake is usually from 10 to50% by weight, preferably from 20 to 40% by weight, based on the wetpress cake.

The crude pigments can be individual chemical compounds but, dependingon the desired result, it is also possible to use mixtures of aplurality of chemical compounds or even solid solutions or mixedcrystals comprising a plurality of chemical compounds, preferablyquinacridones and/or diketopyrrolopyrroles, optionally in combinationwith derivatives thereof. In the selection of components and the amountsthereof, the person skilled in the art will be guided by solid solutionsor mixed crystals that are known per se or to be expected on the basisof the state of the art.

The shuttle mode of operation is especially well suited to thepreparation of pigment mixtures, for example standardisations ofdifferent batches of the same pigment or formulations of a plurality ofpigments. The number of storage vessels is, in such a case, preferablyone more than the number of components to be mixed, which makes itpossible for the treatment period to be matched to the characteristicsof the different components. The person skilled in the art willimmediately recognise the great advantages of this method.

Pigments are, for example, from the 1-aminoanthraquinone, anthanthrone,anthrapyrimidine, azo, azomethine, quinacridone, quinacridonequinone,quinophthalone, dioxazine, diketopyrrolopyrrole, flavanthrone,indanthrone, isoindoline, isoindolinone, isoviolanthrone, perinone,perylene, phthalocyanine, pyranthrone or thioindigo series, optionallyalso in the form of metal complexes or metal lakes. The azos may, forexample, be mono- or dis-azo pigments of all known sub-classes,obtainable, for example, by coupling, condensation or laking.

Pigments conditionable according to the invention are, for example,Colour Index Pigment Yellow 24, 108, 109, 110, 123, 147, 173, 193, 199,Pigment Orange 40, 43, 48, 49, 51, 61, 71, 73, Pigment Red 88, 89, 122,149, 168, 177, 178, 179, 181, 190, 192, 194, 202, 204, 206, 207, 209,216, 224, 226, 254, 255, 262, 264, 270, 272, Pigment Violet 19, 23, 29,31, 37, 42, Pigment Blue 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 60, 64,Pigment Green 7, 36, Pigment Black 31, 32, Vat Red 74,3,6-di(3′-cyano-phenyl)-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione or3-phenyl-6-(4′-tert-butyl-phenyl)-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione.

Preference is given to pigments that do not contain metals. Specialpreference is given to polycyclic pigments, including, especially,quinacridones and dioxazines, and also diketopyrrolopyrroles, veryespecially diketopyrrolopyrroles; quinacridones being preparedpreferably by oxidation of dihydroquinacridones using hydrogen peroxide,for example as described in U.S. Pat. No. 5,840,901 or U.S. applicationSer. No. 60/277,824.

The pigments obtained in accordance with the invention have a highdegree of crystallinity and optimum fastness properties, as well as highcolour strength and colour saturation. Moreover, the particle sizedistribution is astonishingly narrow. In the case of the preferredaverage particle size of the conditioned pigment {overscore (L)} ofpreferably from 0.01 to 3 μm, especially from 0.05 to 2 μm, at least 90%by weight of particles have a size of L±½{overscore (L)} (for example,in the case of an average particle size of 0.2 μm, 0.2±0.1 μm=0.1 to 0.3μm). Especially, at least 80% by weight of particles have a size ofL±¼{overscore (L)}.

A further advantage of the invention is that the crystalline phaseremains substantially unchanged, meaning that the crystalline formidentifiable as the main component in the crude product based on theX-ray powder diagram is also identifiable as the main component in theend product based on the X-ray powder diagram. Generally, when a crudeproduct consists of a mixture of crystalline forms, the proportion ofthe main crystalline form is even increased. Preference is given tocarrying out the method at least until the pigment consists of a singleuniform crystalline form. Depending upon the crude pigment, that may bea pure phase, or a solid solution or a mixed crystal.

The pigments obtained according to the invention can be used for allcustomary purposes, for example for mass-coloration of polymers,including polymers in the form of fibres, surface-coatings (includingspecial-effect paints, including those for the automobile sector) andprinting inks, or also in so-called resists or as toners. Suchapplications will be so evident to the person skilled in the art thatthey need not be listed here. They are also disclosed in referenceworks, for example “Industrielle Organische Pigmente” (W. Herbst+K.Hunger, VCH Weinheim/New York, new editions being continually publishedin German and English).

It is also advantageously possible to prepare both transparent andhiding forms. Especially advantageous is the preparation of hidingpigments, which in contrast to known methods does surprisingly notrequire an acid, base and/or solvent treatment.

The hiding power is suitably measured at in a 25±5 μm thick acrylic orpolyester enamel coating system having a pigment to binder weight ratioof 0.18 over a black and white background and prepared and measuredaccording to established industry procedures such as disclosed inExample 28. For a hiding pigment, the color difference ΔE* measured overa black and white background should be less or equal to 15, preferably≦10, most preferably ≦5.

Transparent pigments generally have a particle size (length) of0.001-0.3 μm, preferably 0.01-0.2 μm, most preferably combined with thenarrow particle size distribution mentioned above. In the same coatingas above, the color difference ΔE* measured over a black background isadvantageously less or equal to 15, preferably ≦10, most preferably ≦5,as compared with the color of the black background itself.

It has furthermore been found, that pigments conditioned in accordancewith the invention are of such outstanding quality that they mayfrequently come into consideration for applications where the qualitiesobtainable hitherto for the same pigment have not been entirelysatisfactory. The person skilled in the art is here expresslyrecommended to carry out appropriate experiments.

The Examples that follow illustrate the invention, without limiting thescope thereof (unless otherwise specified, “%” is always % by weight):

EXAMPLE 1

Pigment Red 255 is prepared in accordance with Example 1 of U.S. Pat.No. 4,579,959, but without drying after the washing water has becomecolourless. In a slurrying vessel made inert with nitrogen, 30 parts byweight of the crude pigment press cake, which is damp with water (40% byweight solids content, 60% by weight water), are dispersed, withstirring, using 9 parts by weight of N-methylpyrrolidone and 81 parts byweight of water for 30 minutes and heated to 74° C. The resultingsuspension, consisting of 10% by weight crude pigment, 7.5% by weightN-methylpyrrolidone and 82.5% by weight water, is circulated through acylindrical wet mill (volume corresponding to 24 parts by weight ofwater) filled to about 80% of its volume with mixed zirconium oxidegrinding elements from 0.3 to 0.4 mm in diameter, at a radial speed of11 m·s⁻¹ and a nominal power output of 1.83 kj·s⁻¹ (net power output1.33 kj·s⁻¹) for 30 minutes at constant temperature. The suspension isthen filtered under suction and washed four times, using 60 parts byweight of water each time. The filtration residue is dried at 87°C./7.1·10³ Pa for 17½ hours and is then grated into small granules usinga Frewitt apparatus. 12 parts by weight of Pigment Red 255 having anarrow particle size distribution and excellent application propertiesare obtained.

EXAMPLE 2

The procedure is analogous to Example 1, but treatment with the wet millis shortened to 20 minutes. The result is very similar to that inExample 1.

EXAMPLE 3

The procedure is analogous to Example 1, but treatment with the wet millis extended to 180 minutes. The result is very similar to that inExample 1.

EXAMPLE 4

The procedure is analogous to Example 1, but with a temperature of 54°C. and a radial speed of 10 m·s⁻¹ in the wet mill. The result is verysimilar to that in Example 1.

EXAMPLE 5

The procedure is analogous to Example 4, but treatment with the wet millis extended to 60 minutes. The result is very similar.

EXAMPLE 6

Pigment Violet 19 is prepared in accordance with Example 1 of U.S. Pat.No. 5,840,901, but without drying after washing with warm water. Usingwater, a portion of the wet press cake containing 33.33 g ofγ-quinacridone is flushed into a storage vessel and slurried (totalweight of the suspension: 400 g). Pigment Red 202 is prepared inaccordance with Example 3 of U.S. Pat. No. 5,840,901, but without dryingafter washing with warm water. Using water, a portion of the wet presscake containing 66.67 g of 2,9-dichloroquinacridone is flushed into astorage vessel and slurried (total weight of the suspension: 600 g).Both storage vessels are heated to 35° C. The γ-quinacridone is thenpassed, via a cylindrical wet mill (volume corresponding to 24 parts byweight of water), filled to about 80% of its volume with mixed zirconiumoxide grinding elements from 0.3 to 0.4 mm in diameter, at a radialspeed of 10 m·s⁻¹, into the 2,9-dichloroquinacridone suspension, and themixture is passed back and forth between the two storage vessels in ashuttle mode of operation for 1 hour. The first storage vessel is thenrinsed with 120 g of N-methylpyrrolidone and a circulating mode ofoperation is carried out using the second storage vessel for a further 1hour at a radial speed of 13.5 m·s⁻¹ and a temperature of 95° C. Theradial speed is then reduced to 4.0 m·s⁻¹ and the suspension is groundfor a further 1 hour in circulating mode. The product is then filteredand washed and dried in customary manner. A quinacridone pigment havinga narrow particle size distribution and excellent application propertiesis obtained.

EXAMPLE 7

1.000 kg of crude Pigment Violet 23 (needles of about length 3 μm andthickness 0.2 μm) is stirred in 8.500 kg of water for 2 hours and then,analogously to the Examples above, transferred to a storage vessel using0.060 kg of N-methylpyrrolidone and heated to 70° C. The suspension iscirculated through a cylindrical wet mill (volume 460 cm³), filled toabout 85% of its volume with yttrium-stabilised mixed zirconium oxidegrinding elements from 0.3 to 0.4 mm in diameter, at a radial speed of12 m·s⁻¹ (speed of rotation 3000 rpm) and a nominal power output of 0.50kj·s⁻¹ for 6 hours at constant temperature. The nominal power output isreduced to 0.1 kj·s⁻¹ (speed of rotation 1800 rpm) and the temperatureis lowered to 25° C. over the course of 1 hour. The suspension isfiltered under suction and washed twice, using 2.0 kg of water eachtime; the product is dried at 80° C./2·10³ Pa. A fine, strongly coloureddioxazine pigment having a narrow particle size distribution and goodapplication properties is obtained.

EXAMPLE 8

The procedure is analogous to Example 7, but 0.900 kg of water and 0.180kg of N-methylpyrrolidone are used. Likewise, a fine, strongly coloureddioxazine pigment is obtained.

EXAMPLE 9

Pigment Red 202 is prepared in accordance with Example 3 of U.S. Pat.No. 5,840,901, but without drying after washing with warm water. Usingwater, a portion of the wet press cake containing 100.0 g of2,9-dichloroquinacridone is flushed into a storage vessel and slurried(total weight of the suspension: 1000 g). The storage vessel is heatedto 35° C. The suspension is then passed, via a cylindrical wet mill(volume corresponding to 24 parts by weight of water), filled to about80% of its volume with mixed zirconium oxide grinding elements from 0.3to 0.4 mm in diameter, at a radial speed of 10 m·s⁻¹, into another,empty storage vessel, and the mixture is passed back and forth betweenthe two storage vessels in a shuttle mode of operation for 1 hour. Thefirst storage vessel is then rinsed with 120 g of N-methylpyrrolidoneand a circulating mode of operation is carried out using the secondstorage vessel for a further 1 hour at a radial speed of 13.5 m·s⁻¹ anda temperature of 95° C. The radial speed is then reduced to 4.0 m·s⁻¹and the suspension is ground for a further 1 hour in circulating mode.The product is then filtered and washed and dried in customary manner. Aquinacridone pigment having a narrow particle size distribution andexcellent application properties is obtained.

EXAMPLE 10

The procedure is analogous to Example 7, but a mixture of 0.750 Kg crude2,9-dichloroquinacridone and 0.250 Kg crude unsubstituted quinacridone(both obtained as coarse particles of specific surface area about 10m²/g by oxydation of the corresponding 6,11-dihydroquinacridones) isused instead of Pigment Violet 23. The isolated product shows excellentapplication properties.

EXAMPLE 11

The procedure is analogous to Example 10, but 180 g of alum followed by27.5 g of quinacridone sulfonic acid are added from 30 min to 20 minbefore end of milling, leading to precipitation of aluminiumquinacridone monosulfonate onto the pigment's surface. The isolatedproduct shows excellent application properties.

EXAMPLE 12

The procedure is analogous to Example 1, but instead of Pigment Red 255,the moist washed press cake of the solid solution of quinacridoneobtained in example 1 of EP 0 894 832 A2 (page 7/line 15) is used anddispersed into a solution composed of 81% of water and 9% ofN-methyl-pyrrolidone. The temperature and milling conditions are as inExample 1. The isolated product has a very narrow particle sizedistribution and shows excellent application properties.

EXAMPLES 13-27

The procedure is analogous to Example 11, but the solid solution ofquinacridone obtained in example 1 of EP 0 894 832 A2 is replaced by themoist press cakes obtained in Examples 1, 2, 3, 4, 5, 6, 7, 8, 9, 11,12, 13, 14, 15 and 16 of EP 0 643 110 A1. The isolated products haveexcellent application properties.

EXAMPLE 28

The pigment according to Example 1 is incorporated into an automotivepolyester/CAB enamel paint system.

(a) Binder solution (8.2% Binder):

-   41.0 CAB® 531.1 (Eastman Chem.), 20% in butyl acetate/xylene 2:1-   1.5 NUODEX® 6 (zirkonium octoate, Nordmann, Rassmann, D-Hamburg)-   18.5 Solvesso® 150 (Exxon)-   21.5 butyl acetate-   17.5 xylene    (b) Millbase Formulation:

A 250 ml jar is charged with 15.73 g Dynapol® H 700-08 (Degussa-Hüls),11.80 g of the freshly prepared binder solution from (a), 11.80 gMaprenal® MF 650 (Vianova Resins) and 2.67 g dispersant Disperbyk® 161(BYK Chemie). 8 g pigment according to Example 1 and 100 g of glassbeads are added. The mixture in the jar is shaken on a Skandex shakerfor 1 hour. The millbase contains 16.0% pigment with a pigment/binderratio of 1:2.25 and a solids (pigment+binder) content of 59%.

(c) Masstone Color for an PES/CAB Enamel Drawdown:

23.75 g of the millbase from (b), 10.50 g of Dynapol® H 700-08, 7.87 gof the binder solution from (a) and 7.87 g Maprenal® MF 650 are mixed,yielding a resin/pigment dispersion with a concentration of 7.6% pigmentin a pigment to binder ratio of 1:5.22 and a solid (pigment+binder)content of 47.3%.

(d) Coating:

The resin/pigment dispersion is drawn down onto a Leneta black and whitechart from the Leneta Company using a 100 μm wet film applicator. Thefilm is flashed in a flash cabinet for 30 minutes and then “baked” in anoven at 130° C. for 30 minutes. The final thickness of the coating is 28μm.

(e) Colour Measurement:

The C.I.E. L*, C*, h color space values are obtained from the portionover white background using a D₆₅ illuminant and 10° observer with aspecular component included.

EXAMPLES 29-54

The procedure is analogous to Example 28 (a)-(e), but the pigment ofExample 1 is replaced by the pigments of Examples 2-27.

1. A method for the preparation of a conditioned organic pigment,comprising the steps wherein (1) a pigment suspension is formed throughsynthesis of an organic pigment in a liquid reaction medium andprecipitation of the thus synthesized pigment from said liquid reactionmedium; (2) the pigment suspension from step (1) is transferred into astorage vessel, keeping the pigment surface substantially wettedthroughout the transfer with said liquid reaction medium, a washingagent, a polar liquid or water; (3) if the liquid medium of the pigmentsuspension in the storage vessel does not already consist of water andfrom 1 to 30% by weight of a neutral, polar liquid, based on the totalamount of liquid and water, the composition of the pigment suspension isso modified by means of the addition of water and/or neutral, polarliquid having a dipole moment μ of 2.8-6.0·10⁻¹⁸ esu so that the amountof neutral, polar liquid is from 1 to 30% by weight, based on the totalamount of liquid and water; (4) the pigment suspension from the storagevessel is passed a number of times through an agitated media pearl millhaving a radial speed in a circulating or shuttle mode of operation, theagitated media pearl mill having a smaller chamber volume than thevolume of the pigment suspension and being operated at a specific powerdensity of at most 2.0 kJ·s⁻¹ per liter of grinding space; (5) thepigment is isolated by removing the liquid surrounding it.
 2. A methodfor the preparation of a conditioned organic pigment according to claim1, further comprising one or more steps selected from the groupconsisting of increasing the concentration of pigment in the pigmentsuspension after step (1) and before step (5) by removing part of theliquid reaction medium; adding a washing agent to the pigment suspensionafter step (1) and before step (5); and adding one or more additionalsubstances selected from the group consisting of acids, bases, resins,growth inhibitors, dispersing agents, and wetting agents during any stepprior to step
 5. 3. A method according to claim 1 wherein the neutral,polar liquid has a dipole moment μ of 3.3-5.5·10⁻¹⁸ esu.
 4. A methodaccording to claim 1, wherein the neutral, polar liquid is one or morecompounds selected from the group consisting of acetamide, formamide,methylacetamide, methylformamide, caprolactam, valerolactam,1,1,2,2-tetramethylurea, dimethyl sulfoxide, sulfolane, nitromethane,nitrobenzene, acetonitrile, methanol, ethylene carbonate,dimethylacetamide, dimethylformamide and N-methylpyrrolidone.
 5. Amethod according to claim 1, wherein the amount of neutral, polar liquidis from 3 to 20% by weight based on the total amount of liquid andwater.
 6. A method according to claim 1, wherein the pigment is aquinacridone, dioxazine or diketopyrrolopyrrole pigment.
 7. A methodaccording to claim 1, wherein the total treatment period in the agitatedmedia pearl mill is from 20 to 200 minutes.
 8. A method according toclaim 7, wherein after two-thirds of the total treatment period, theradial speed is adjusted to a value of at most 11 m·s⁻¹.
 9. A methodaccording to claim 1, wherein the pigment obtained in step (5) consistsof at least 90% by weight of particles having a size of L±½{overscore(L)}, wherein the average particle size {overscore (L)} is from 0.01 to3 μm.
 10. A method according to claim 1, wherein the pigment obtained instep (5) has hiding power leading to a color difference ΔE* less orequal to 15, as measured in a 25±5 μm thick acrylic or polyester enamelcoating system having a pigment to binder weight ratio of 0.18 over ablack and white background.
 11. A method according to claim 1, whereinthe pigment obtained in step (5) is transparent and has a particle sizeof 0.001-0.3 μm.
 12. A method according to claim 1, wherein the pigmentis a diketopyrrolopyrrole pigment.
 13. A method according to claim 1wherein the neutral, polar liquid has a dipole moment μ of 3.8-5.0·10⁻¹⁸esu.
 14. A method according to claim 7, wherein after two-thirds of thetotal treatment period, the radial speed is adjusted to a value of from1 to 8 m·s⁻¹.
 15. A method according to claim 7, wherein aftertwo-thirds of the total treatment period, the radial speed is adjustedto a value of from 2 to 5 m·s⁻¹.
 16. A method according to claim 1,wherein the pigment obtained in step (5) has hiding power leading to acolor difference ΔE* less or equal to 10, as measured in a 25±5 μm thickacrylic or polyester enamel coating system having a pigment to binderweight ratio of 0.18 over a black and white background.
 17. A methodaccording to claim 1, wherein the pigment obtained in step (5) hashiding power leading to a color difference ΔE* less or equal to 5, asmeasured in a 25±5 μm thick acrylic or polyester enamel coating systemhaving a pigment to binder weight ratio of 0.18 over a black and whitebackground.
 18. A method for the preparation of a conditioned organicpigment comprising the steps wherein (1) a pigment suspension is formedthrough synthesis of an organic pigment in a liquid reaction medium andprecipitation of the thus synthesized pigment from said liquid reactionmedium; (2) the pigment from step (1) is filtered and optionally washedto form a press cake; (3) the press cake from step (2) is dried to forma crude pigment having a specific surface area of from 1 to 25 m²/g, thedried crude pigment optionally still comprising a residual amount ofwater and/or a neutral, polar liquid; (4) the crude pigment from step(3) is transferred into a storage vessel and wetted with addition ofwater and/or a neutral, polar liquid having a dipole moment μ of2.8-6.0·10⁻¹⁸ esu; (5) if the liquid phase of the pigment suspension inthe storage vessel does not already consist of water and from 1 to 30%by weight of a neutral, polar liquid, based on the total amount ofliquid and water, the composition of the pigment suspension is somodified by means of the addition of water and/or neutral, polar liquidhaving a dipole moment μ of 2.8-6.0·10⁻¹⁸ esu so that the amount ofneutral, polar liquid is from 1 to 30% by weight, based on the totalamount of liquid and water; (6) the pigment suspension from the storageis passed a number of times through an agitated media pearl mill havinga radial speed in a circulating or shuttle mode of operation, theagitated media pearl mill having a smaller chamber volume than thevolume of the pigment suspension and being operated at a specific powerdensity of at most 2.0 kJ·s⁻¹ per liter of grinding space; (7) thepigment is isolated by removing the liquid surrounding it.
 19. A methodfor the preparation of a conditioned organic pigment according to claim18, further comprising one or more steps selected from the groupconsisting of adding a substance selected from the group consisting ofacids, bases, resins, growth inhibitors, dispersing agents, and wettingagents during any step prior to step 7; adding a washing agent to anypigment suspension obtained prior to step (7); and increasing theconcentration of pigment in the pigment suspension by removing part ofthe liquid medium between steps (6) and (7) or after addition of awashing agent.
 20. A method according to claim 18, wherein the neutral,polar liquid has a dipole moment μ of 3.3-5.5·10⁻¹⁸ esu.
 21. A methodaccording to claim 18, wherein the neutral, polar liquid is one or morecompounds selected from the group consisting of acetamide, formamide,methylacetamide, methylformamide, caprolactam, valerolactam,1,1,2,2-tetramethylurea, dimethyl sulfoxide, sulfolane, nitromethane,nitrobenzene, acetonitrile, methanol, ethylene carbonate,dimethylacetamide, dimethylformamide and N-methylpyrrolidone.
 22. Amethod according to claim 18, wherein the amount of neutral, polarliquid is from 3 to 20% by weight based on the total amount of liquidand water.
 23. A method according to claim 18, wherein the pigment is aquinacridone, dioxazine or diketopyrrolopyrrole pigment.
 24. A methodaccording to claim 18, wherein the total treatment period In theagitated media pearl mill is from 20 to 200 minutes.
 25. A methodaccording to claim 24, wherein after two-thirds of the total treatmentperiod, the radial speed is adjusted to a value of at most 11 m·s⁻¹. 26.A method according to claim 18, wherein the pigment obtained in step (7)pigment consists of at least 90% by weight of particles having a size ofL±½{overscore (L)}, wherein the average particle size {overscore (L)} sfrom 0.01 to 3 μm.
 27. A method according to claim 18, wherein thepigment obtained in step (7) has hiding power leading to a colordifference ΔE* less or equal to 15, as measured in a 25±5 μm thickacrylic or polyester enamel coating system having a pigment to binderweight ratio of 0.18 over a black and white background.
 28. A methodaccording to claim 18, wherein the pigment obtained in step (7) istransparent and has a particle size of 0.001-0.3 μm.
 29. A methodaccording to claim 18, wherein the pigment is a diketopyrrolopyrrolepigment.
 30. A method to according to claim 18, wherein the neutral,polar liquid has a dipole moment μ of 3.8-5.0·10⁻¹⁸ esu.
 31. A methodaccording to claim 24, wherein after two-thirds of the total treatmentperiod, the radial speed is adjusted to a value of from 1 to 8 m·s⁻¹.32. A method according to claim 24, wherein after two-thirds of thetotal treatment period, the radial speed is adjusted to a value of from2 to 5 m·s⁻¹.
 33. A method according to claim 18, wherein the pigmentobtained in step (5) has hiding power leading to a color difference ΔE*less or equal to 10, as measured in a 25±5 μm thick acrylic or polyesterenamel coating system having a pigment to binder weight ratio of 0.18over a black and white background.
 34. A method according to claim 18,wherein the pigment obtained in step (5) has hiding power leading to acolor difference ΔE* less or equal to 5, as measured in a 25±5 μm thickacrylic or polyester enamel coating system having a pigment to binderweight ratio of 0.18 over a black and white background.